JEE Advanced · Physics · 27. Atomic Physics
Paragraph:
When a particle is restricted to move along \(x\)-axis between \(x=0\) and \(x=a\), where \(a\) is of nanometer dimension, its energy can take only certain specific values. The allowed energies of the particle moving in such a restricted region, correspond to the formation of standing waves with nodes at its ends \(x=0\) and \(x=a\). The wavelength of this standing wave is related to the liner momentum \(p\) of the particle according to the de Broglie relation. The energy of the particle of mass \(m\) is related to its linear momentum as \(E=\frac{p^2}{2 m}\). Thus, the energy of the particle can be denoted by a quantum number \(n\) taking values \(1,2,3, \ldots(n=1\), called the ground state) corresponding to the number of loops in the standing wave.
Use the model described above to answer the following three questions for a particle moving in the line \(x=0\) to \(x=a\) [Take \(h=6.6 \times 10^{-34} \mathrm{Js}\) and \(e=1.6 \times 10^{-19} \mathrm{C}\) ]
Question:
If the mass of the particle is \(m=1.0 \times 10^{-30} \mathrm{~kg}\) and \(a=6.6 \mathrm{~nm}\), the energy of the particle in its ground state is closest to
- A \(0.8 \mathrm{meV}\)
- B \(8 \mathrm{meV}\)
- C \(80 \mathrm{meV}\)
- D \(800 \mathrm{meV}\)
Answer & Solution
Correct Answer
(B) \(8 \mathrm{meV}\)
Step-by-step Solution
Detailed explanation
From Eq. (i)
\(E=\frac{n^2 h^2}{8 a^2 m}\)
In ground state \(n=1\)
\(\therefore E_1=\frac{h^2}{8 m a^2}\)
Substituting the values, we get
\(E_1=8 \mathrm{meV}\)
\(E=\frac{n^2 h^2}{8 a^2 m}\)
In ground state \(n=1\)
\(\therefore E_1=\frac{h^2}{8 m a^2}\)
Substituting the values, we get
\(E_1=8 \mathrm{meV}\)
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